Claude Fable 5.1 vs GPT-5.5 vs GPT-6 Astra
Too close to call on our weighted score (GPT-6 Astra 68, Claude Fable 5.1 66, GPT-5.5 63). The right pick depends on what you value most.
AnthropicClaude Fable 5.1
66/100- ECI164.8
- Price$10.00 / $50.00
- Context1M
OpenAIGPT-5.5
63/100- ECI159.2
- Price$5.00 / $30.00
- Context1.05M
- OpenAI
GPT-6 Astra
68/100- ECI166.5
- Price$10.00 / $50.00
- Context1.05M
Too close to call
It is close. Our weighted score puts them within 1 points (GPT-6 Astra 68/100, Claude Fable 5.1 66/100, GPT-5.5 63/100), so choose by what matters most for your work: GPT-6 Astra for raw capability and GPT-5.5 on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityGPT-6 AstraCapabilities Index (ECI): GPT-6 Astra 166.5 · Claude Fable 5.1 164.8 · GPT-5.5 159.2
- Lowest priceGPT-5.5GPT-5.5 $11.25 · Claude Fable 5.1 $20.00 · GPT-6 Astra $20.00 per 1M tokens (3:1 blend)
- Longest contextGPT-5.5 and GPT-6 AstraGPT-5.5 1,050,000 · GPT-6 Astra 1,050,000 · Claude Fable 5.1 1,000,000 tokens
- Widest inputsSame inputsClaude Fable 5.1: Text, Images, PDFs · GPT-5.5: Text, Images, PDFs · GPT-6 Astra: Text, Images, PDFs
- Self-hostingNo open weightsAll three are available only through APIs
| Measure | Weight | Claude Fable 5.1 | GPT-5.5 | GPT-6 Astra |
|---|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 97 | 90 | 99 |
| Price | 25% | 0 | 0 | 0 |
| Inputs & features | 15% | 80 | 80 | 80 |
| Context window | 10% | 60 | 61 | 61 |
| Overall | 100% | 66/100 | 63/100 | 68/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | Claude Fable 5.1Anthropic | GPT-5.5OpenAI | GPT-6 AstraOpenAI |
|---|---|---|---|
| Capability | |||
| Capabilities Index (ECI) | 164.8 | 159.2 | 166.5 (best) |
| ECI rank | #4 of 148 | #10 of 148 | #2 of 148 (best) |
| GPQA DiamondGraduate-level science questions | — | 94.0% | 95.8% (best) |
| FrontierMath Tiers 1–3Research-level mathematics | 90.2% | 85.3% | 93.7% (best) |
| OTIS Mock AIME 2024–2025Competition mathematics | 100% | 100% | 100% |
| SWE-bench VerifiedFixing real GitHub issues | — | 80.6% | — |
| SimpleQA VerifiedShort factual questions | 70.8% | 63.0% | 75.6% (best) |
| Price per million tokens | |||
| Input | $10.00 | $5.00 (best) | $10.00 |
| Output | $50.00 | $30.00 (best) | $50.00 |
| Cached input | $0.25 (best) | $0.50 | $1.00 |
| Blended (3:1) | $20.00 | $11.25 (best) | $20.00 |
| Long-context rate | Same rate | Over 272K: $10.00 / $45.00 | Over 272K: $20.00 / $75.00 |
| Price source | Official Anthropic API | Official OpenAI API | Official OpenAI API |
| Limits | |||
| Context window | 1,000,000 tokens | 1,050,000 tokens (best) | 1,050,000 tokens (best) |
| Max output | 128,000 tokens | 128,000 tokens | 128,000 tokens |
| Inputs and features | |||
| Text | Yes | Yes | Yes |
| Images | Yes | Yes | Yes |
| PDFs | Yes | Yes | Yes |
| Audio | No | No | No |
| Video | No | No | No |
| Reasoning | Yeslow · medium · high · xhigh · max | Yeslow · medium · high · xhigh | Yeslow · medium · high · xhigh · max |
| Tool calling | Yes | Yes | Yes |
| Structured output | Yes | Yes | Yes |
| Availability | |||
| Weights | Proprietary | Proprietary | Proprietary |
| API model ID | claude-fable-5-1 | gpt-5.5 | gpt-6-astra |
| API providers | 29 | 42 (best) | 26 |
| Released | Sep 1, 2026 | Apr 23, 2026 | Sep 4, 2026 |
| Knowledge cutoff | Jun 2026 | Dec 1, 2025 | Apr 30, 2026 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- Claude Fable 5.1$200.00
- GPT-5.5$110.00
- GPT-6 Astra$200.00
Which should you choose?
Which is better: Claude Fable 5.1, GPT-5.5 or GPT-6 Astra?
It is close. Our weighted score puts them within 1 points (GPT-6 Astra 68/100, Claude Fable 5.1 66/100, GPT-5.5 63/100), so choose by what matters most for your work: GPT-6 Astra for raw capability and GPT-5.5 on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, Claude Fable 5.1, GPT-5.5 or GPT-6 Astra?
GPT-5.5 is cheaper at $5.00 input / $30.00 output per million tokens (official OpenAI API price). Claude Fable 5.1 costs $10.00 input / $50.00 output per million tokens (official Anthropic API price); GPT-6 Astra costs $10.00 input / $50.00 output per million tokens (official OpenAI API price). At a typical mix of three input tokens to one output token, that is $11.25 per million tokens for GPT-5.5 versus $20.00 for Claude Fable 5.1 (1.8× as much) and $20.00 for GPT-6 Astra (1.8× as much).
Which scores higher on benchmarks?
GPT-6 Astra scores higher on the Capabilities Index (ECI): GPT-6 Astra 166.5 (#2 of 148), Claude Fable 5.1 164.8 (#4 of 148) and GPT-5.5 159.2 (#10 of 148). The confidence ranges of the top two overlap (163.1–171.1 vs 161.8–169.1), so treat the gap as small. On individual benchmarks: FrontierMath Tiers 1–3 — GPT-6 Astra 93.7%, Claude Fable 5.1 90.2%, GPT-5.5 85.3%; OTIS Mock AIME 2024–2025 — Claude Fable 5.1 100%, GPT-5.5 100%, GPT-6 Astra 100%; SimpleQA Verified — GPT-6 Astra 75.6%, Claude Fable 5.1 70.8%, GPT-5.5 63.0%.
Which is better for coding?
There are no published SWE-bench Verified results for Claude Fable 5.1 and GPT-6 Astra yet, so there is no like-for-like coding score. On overall capability, GPT-6 Astra leads, which tends to carry over to coding, but test on your own codebase. All three support tool calling for agent workflows.
Which has the bigger context window?
GPT-5.5 and GPT-6 Astra have the largest context windows (1,050,000 and 1,050,000 tokens), against 1,000,000 for Claude Fable 5.1. Maximum output per response: Claude Fable 5.1 up to 128,000, GPT-5.5 up to 128,000, GPT-6 Astra up to 128,000 tokens.
Which can read images, PDFs, audio or video?
Claude Fable 5.1 accepts text, images and PDFs; GPT-5.5 accepts text, images and PDFs; GPT-6 Astra accepts text, images and PDFs. They handle the same number of input types.
Are any of these open source?
No. Claude Fable 5.1, GPT-5.5 and GPT-6 Astra are proprietary and only available through APIs and apps.
Which is newer?
GPT-6 Astra is the newest, released Sep 4, 2026. Claude Fable 5.1 came out Sep 1, 2026; GPT-5.5 came out Apr 23, 2026. Knowledge cutoff: Claude Fable 5.1 Jun 2026, GPT-5.5 Dec 1, 2025, GPT-6 Astra Apr 30, 2026.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
